1. Field of Invention
The present invention relates to an ink supply unit for supplying ink to an ink jet head in an ink jet recorder.
2. Description of Related Art
In a conventional ink supply mechanism used with an ink jet recorder, an ink tank contains a porous member with one end coupled to a print head via a filter and the other end formed with an air inlet, for example, as described in Japanese Patent Examined Publication No. Hei 3-41351. In such an ink supply mechanism, air may enter the filter through the space between the porous member and the inner wall of the ink tank, inhibiting ink supply to the ink tank.
To solve such a problem, for example, in Japanese Patent Unexamined Publication No. Hei 2-34354, such a rib abutting an ink absorber is placed on the inner wall face of an ink tank for preventing bubbles from entering a head. However, also in this method, adhesion of the head to a sponge may be poor and air still enters the head along the inner wall face of the ink tank.
As alternative solution means, for example, an air gathering chamber containing a porous member is disposed in anink flow path connecting a print head and an ink vessel for gathering bubbles, as disclosed in Japanese Patent Unexamined Publication No. Sho 57-2786. However, in such a structure, flow path resistance of the porous member itself is large and when bubbles build up on full surfaces of the porous member, flow path resistance increases and ink supply does not keep pace with ink required for responding to high-speed printing.
Further, for example, a filter cloth is stuck on one face of an elastomer plate having a through hole for gathering bubbles on the filter face, as disclosed in Japanese Patent Unexamined Publication No. Sho 59-95152. However, also in this structure, when bubbles build up on full surfaces of the filter cloth, flow path resistance increases and ink supply does not keep pace with ink required for responding to high-speed printing, as in the above-mentioned structure.
Further, for example, a hollow needle is used for a joint connecting an ink tank and a head and a porous substance is disposed in the hollow needle for preventing the entry of bubbles or dust, as disclosed in Japanese Patent Unexamined Publication No. Hei 3-189157. However, in this structure, the inner diameter of the hollow needle needs to be made small virtually to provide a good connection property of the joint. That is, since the opening area of the porous member contained in the hollow needle lessens, flow path resistance increases and ink supply does not keep pace with ink required for responding to high-speed printing.
In such a structure wherein bubbles are trapped on the faces of the porous substance or the filter, it is also possible to enlarge the filter particle size of the porous substance or the filter to decrease the flow path resistance. In this case, for example, if a large amount of ink is consumed because of maintenance, etc., bubbles pass through the porous substance or the filter and enter the print head, causing print failure, etc.
As another art, a method wherein ink is stored in a subtank disposed between an ink tank and a head and is supplied from the subtank to the head is disclosed, for example, in Japanese Patent Laid-Open No. Sho 60-262654. The subtank is opened to the atmosphere and bubbles and ink are separated in the subtank for supplying only ink to the head. However, in this structure, there is a possibility that ink will leak from the atmospheric release port of the subtank and further there is a restriction on design that the head is placed above the subtank to maintain ink pressure at negative pressure.